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Lecture

Sun and Its Neighbours oct 15th 2013.docx


Department
Astronomy & Astrophysics
Course Code
AST101H1
Professor
Michael Reid

Page:
of 4
Sun and Its Neighbours oct 15th 2013
KNOWING LIGHT IS MADE UP FROM ELECTRO MAGNETIC
FIELDS THEY HAVE A SHAPE TO THEM, WAYS OF
DESCRIBING LIGHT AS A WAVE LENGTH, HOW BIG IS THE
WAVE, THIS IS VERY SIMPLE PERAMITER, THE LENGTH OF A
WAVE, IS THE DISTANCE FRMO TWO ADJACENT PEEKS OR
TROUGHTS TWO LOW POINTS OR HIGH POINTS OF THE
WAVE, THE DIFFERENCE IS THE LENGTH OF WAVE.
all that changes in light is the wave length, all light travels at the same
speed (in empty space). in a vacuum
The vacuum I'm talking about is the emptiness of space, all light travels
at the same fix speed, of the emptiness of space, whether your or ax
ray or a radio wave, two opposite ends of wave length regime both
them move the same way, when light enters material objects like air
window, or lead, it will cnhage its speed, when we refer to the speed of
light were explicitly adding in a vacuum, how fast is that.
the speed of light: c = 300,000,000 m/s
that is the speed of light in a vacuum, if you put light in things you can
slow it down quite a bit.
we can slow down in material objects, if you put light in anything it
slows down.
as far as we know no you can't, light can't go faster then that.
Our eyes perceive different wavelengths as different colours.
we perceive wavelengths as human beoings as different colour, colour
is the property of the human brian, colour is how we perceive different
wave lengths of life. this is the way we perceive colour, we perceive
short waves length as blue, and long wave lengths as red, colour
present and absent, blue green yellow orange red, theres no pink brown
black purple…
some of the colours you perceive, aren to actual clots associated with
wave lengths of light, it makes all intermediate colours, by mixing
those colours in various amounts.
wavelength speed and frequency are related because light always has
the same speed, that speed in physics and astronomy that we label as c,
its a fixed number, since its a fixed number i can't get rid of it. the wave
length of light is proportional to 1 over the frequency, ' we can finish
entire rest of course with out thinking of frequencies,
since you'll encounter both terms there the inverse of one another red
small eve length blue is large shortest wave length is blue, their the
opposite of one another
clicker quiz which colour of light has the highest frequency is blue.
shortest wave length frequency and wave length are related because of
in verse, shortest wave length smallest wave length should mean same
thing as highest frequency 92% said D. blue.
-Collectively we refer to all possible wavel lengths of light as electro
magnetic spectrum, very short wave length light called gamma rays
short is radio waves, x ray different from radio wave etc. all different
wave lengths.
with in visible part of spectrum web ave rainbow you can see, all are
invisible to eyes except visible .
bluer light has higher energy, refer light has lower energies
often conventionally we reefer to light as long wave length of spectrum
as "redder" frequency energy eve length and bluer redder to describe
light.
a cosmic ray is a particle of matter, a proton, or electron, not a wave
length of light
radio waves are a signal that encodes a sound, a radio takes a radio light
and converts it in to sound so you can hear it, radio waves have nothing
to do with sound entrinsicly.
We can use a Spectrograph to spread the light from
it produces a spectrum, this is a simple light spectrograph, some source
of pure white light which is a light bulb, we pass it through a slit which
gets you a nice narrow been, through a glass or plastic pass through a
certain way, you guys are familiar with doing this, see lighs passing
through rainbow at home.
We can display a spectrum as either an image or graph. display things
as actual spectrum of light, convert picture in to graph.
in this image on top or bottom you see the same information, on top
your seeing a picture of a spectrum, you have equal amount of all the
colours from violet to red, your not missing yellow, you have equal
amounts of all wave length, if we draw a graph of light intensity among
wave length, on that graph this spectrum is a flat line, equal amount of
all colours.
how can you tell if c is correct or not for this clicker quiz
you can tell c is correct because you don't see the same colour twice,
according to c the amount of light on this side is the same as the
amount of light on that side? true no. lots of light on one side no light
on other, it has to be A its the only one that works.
I lined up this graph in the image here that image would produce that
graph, that is a natural phenomenon, nothing in nature makes that
graph, in nature we more often see this, this is a very important kind of
spectrum, which we call a black body spectrum, its everywhere in
nature, if you look at that object represented in that spectrum what clot
do you think it may look to your eye, the thing that is producing that
spectrum, your idea picks up all colros at once, which one would it be,
the green because thats where the peek is is, the sun is emitting more
green lgith than any other, you get a white sum, some of every colour,
both different spectres, are what we call a continuous spectra, their not
missing any colour there is no gap.
In reality the spectrum of the sun is not continuous its full of tin gaps…
this particular form of a continuous spectrum any continuous length a
straight line up, any unbroken line is called continuous, this line is a
black body spectrum, pg 40, the kind of things that make this spectrum
heres the key thing Anything DENSE OBJECTS, whether solid, liquid,
gas or plasma, emit light according to that blackbody spectrum.
pressure temperature, chemical composition how its moving , how old
it is moving else matters, if its dense it produces black body spectrum,
all that changes for different t black body spectrum, is they change
according to the temperature of the object, the visible part of the
spectrum, has been coloured in by a rainbow, lines bend dawn on
indicating black bodies of different temperatures, the colour of o the
line indicates what colour of object would occur to your eye,we can see
invisible light how do we know how can we test whether were
producing visible lights, if we turn off lights I'm glowing I'm the visible
light. i am emitting light, I'm just not emitting visible light, I'm emitting
infra red light, those stars are red yellow blue because of amount of
light their emitting.